This invention relates to the alkylation of phenolic compounds. In accordance with another aspect, this invention relates to the alkylation of phenols wherein the principal substitution is in the ortho-ring position. In another aspect, this invention relates to the liquid phase alkylation of phenols with alcohols in the presence of a catalyst selected for the production of ortho-substituted phenolic products. In accordance with a further aspect, this invention relates to the alkylation of phenols using a boron trifluoride etherate catalyst wherein the principal substitution is in the ortho-ring position.
The alkylation of phenols with alcohols, alkyl halides and olefins is old per se. It is further known and recognized that the benzene nucleus in phenolic compounds is very susceptible to alkylation in the presence of conventional alkylation catalysts such as sulfuric acid, aluminum chloride, zinc chloride, hydrogen fluoride and the like. However, this very ease of alkylation often is a disadvantage when the synthesis of specific monoalkylated derivatives of phenols are desired. Further complications involved in phenl alkylation are attributed to the reactivity of the phenolic group toward alkylating agents giving rise to undesirable aralkylethers. Thus, in the alkylation of phenol and cresols with butyl alcohol or butylenes, for example, the art shows yields of monoalkyl derivatives seldom exceeding 50 mole percent and more often in the neighborhood of 30-40 percent. The balance of the products in such cases are aralkyl ethers and polysubstituted phenols.
The use of boron fluoride or, more precisely, the complex of boron trifluoride and orthophosphoric acid is described in U.S. Pat. No. 2,544,818 as a catalyst for the alkylation of phenol with an olefin such as propylene to give a mixture of ortho- and para-isopropylphenol. No mention is made of the selectivity of the products. However, the reaction which is run in a paraffin solvent requires a water wash followed by an aqueous alkali extraction prior to distillation.
A further reference, "Friedal-Crafts and Related Reactions", by George Olah, Vol. II, Part I, page 566, discloses a process of alkylating phenol with isopropyl alcohol using a boron trifluoride catalyst to give yields of 32% ortho-isopropylphenol, 16% para-isopropylphenol and 13% 2,4-diisopropylphenol isopropyl ether. This is a 52% selectivity of ortho-isopropylphenol.
Several additional references disclose the vapor phase alkylation of phenols with alcohols to give ortho alkylated phenols. All of these references employ other type catalyst and report reaction conditions above 200.degree. C. This cited art is U.S. Pat. Nos. 3,707,569; 3,751,488; 3,764,630; and 3,972,836.
Thus, it would be advantageous if mono orthosubstituted phenols could be prepared in high yields and high selectivity. It would also be of some economic advantage if the desired product could be easily separated and purified without employing additional operations such as washings, etc.
An object of this invention is to provide an improved process for the alkylation of phenols with alcohols.
Another object of this invention is to provide a process of producing ortho-alkylated phenols in high yields and high selectivity.
A further object of this invention is to provide a catalyst selective for the production of ortho-alkylated phenols.
Other objects, aspects, and the several advantages of this invention will become apparent to one skilled in the art upon reading the specification and appended claims.